Some code snippets demonstrating mixing of static and non-static contexts in PHP

static-non-static-mixing.php

<?php
class Foo {
	public static function bar() {
		echo "calling public static bar() in an ".(isset($this)?"object (".get_class($this).")":"static")." context. \n";
	}
	public function baum() {
		echo "calling public baum in an ".(isset($this)?"object (".get_class($this).")":"static")." context. \n";
	}
}

class Thief {
	public function meow() {
		Foo::bar();
		Foo::baum();
	}
}

$foo=new Foo;
$t=new Thief;

echo "[0]\n";
Foo::bar();
echo "[1]\n";
$foo->bar();

echo "[2]\n";
Foo::baum();
echo "[3]\n";
$foo->baum();

echo "[4]\n";
Thief::meow();
echo "[5]\n";
$t->meow();

//$t->Foo::baum();
/*
This would create the most famous PHP error message: 
PHP Parse error:  syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in /home/amoebe/static.php on line 37
*/
//call_user_func(array($t,'Foo::baum'));
/*
This fails too:
PHP Warning:  call_user_func() expects parameter 1 to be a valid callback, class 'Thief' is not a subclass of 'Foo' in /home/amoebe/static.php on line 42
*/

/*
Output:

[0]
calling public static bar() in an static context.
[1]
calling public static bar() in an static context.
[2]
calling public baum in an static contiext.
[3]
calling public baum in an object (Foo) context.
[4]
calling public static bar() in an static context.
calling public baum in an static context.
[5]
calling public static bar() in an static context.
calling public baum in an object (Thief) context.

*/
?>

One oddity in PHP is that you can call static methods like 
non-static and the other way around. 

The only differnce is: When calling a method explicitly
declared as static you will be in a static context even 
if the call looks like $object->method(), see [1]. 

Another surprising behaviour is calling foreign methods
in an non-static context, but with the static syntax, like
OtherClass::otherMethod() in $classInstance->method(). 
They will actually be called like own methods even having 
the current obejct as $this availible, 
see [5].
Reasonably, you can access $this, but not private/protected 
properties in the foreign class. And you can't summon this 
magic form outside the object's methods.